1. Field of the Invention
This invention relates to fluid flow devices and in particular to means for selectively closing an opening in a fluid conducting means.
2. Description of the Prior Art
In U.S. Pat. No. 1,708,907 of Ira H. Spencer, a check valve is shown having spring means for biasing closure members outwardly from a folded arrangement. A pair of springs is provided for association one each with the closure members and each of the springs is maintained spaced from the closure member between the closed position and the fully open position wherein the closure members extend generally parallel to the flow direction.
Robert M. Sherman et al disclose, in U.S. Pat. No. 2,827,921, a low torque instant closing check valve having a spring-biased closing mechanism causing maximum closing force to be exerted on the valve member in the closed position and with the biasing force diminishing as an incident of the movement of the valve from the closed position toward the open position. In the closed position, a relatively small spring pressure of the partially extended spring means is applied substantially fully in a direction tending to straighten out the links of the mechanism and results in a valve closing pressure which is much larger than the spring pressure. In the open arrangement of the valve, the relatively larger spring pressure of the more extended springs tends to straighten out the links resulting in a reduced valve closing pressure.
In U.S. Pat. No. 3,009,473 of Joseph W. Hennen, a snap-in damper is illustrated utilizing a pair of springs extended about a beam at the axis of the damper and having their opposite ends connected to the damper members. The opposite ends of the springs are secured directly to the damper members and the mid-portion of the springs is bowed out by the axial beam.